The present invention relates to an immersible heater for an aquarium; and more particularly, the invention relates to such a heater which includes an electric heating element and a temperature controller, both being contained in a housing or the like.
Heaters of the type to which the invention pertains are used to a rather large extent. The housing is usually of a tubular configuration and is, preferably, made of glass; but metal tubes have been used in some instances. These heaters are by and large acceptable, but particularly glass tubes are prone to damage. Also, the interface between the heater and the surrounding liquid is rather small; increasing the area of that interface requires a larger diameter or a larger length (or both). A larger diameter tube is undesirable for reasons of strength (glass!). Also, a larger tube generally will occupy more space that is lost for the intended purpose of the aquarium. Also, the length of the heater tube is limited by the height of the aquarium.
In view of the foregoing, it seems apparent that a larger heating power requires a higher temperature of the heater. That, however, is undesirable since it may lead to unduly high temperature gradients inside the aquarium.